Method and Distance Detecting Device for Detecting the Projected Distance Between a Distance Measuring Device and an Obstacle

ABSTRACT

The invention relates to method and a device for determining the projected distance between a distance measuring device and a nearest point on the surface of an obstacle, the projected distance between said point and the distance measuring device being fundamentally the shortest in relation to all points of the obstacle. The aim of the invention is to be able to calculate the current distance between the nearest point and the distance measuring device, when the point P is no longer inside the detection region of the distance measuring device. According to the invention, the calculation of the projected distance is based on information about the relative movement of the distance measuring device and the obstacle, and on a defined limiting distance.

The invention concerns a method for detecting the projected distancebetween a distance measuring device, which is preferably installed in avehicle, and an obstacle. The invention also concerns a computer programincluding a program code and a distance detecting device for performingthis method.

Methods and devices of this type are known in the art. Any obstacle hasone nearest point on the surface of the obstacle in the vicinity of thedistance measuring device, having the shortest projected distance fromthe distance measuring device of all points on the obstacle. Thisshortest projected distance is detected by conventional methods anddevices, when and for as long as the nearest point is within thedetecting range of the distance measuring device. Distance measuringdevices, which are installed e.g. in vehicles, with horizontalorientation and a conical detecting range, bear the risk that obstacleshaving a maximum height, which is smaller than the height of theinstallation position of the distance measuring device, disappear fromthe conical detecting range below a certain minimum separation.

Departing therefrom, it is the underlying purpose of the invention toprovide a method for detecting the shortest projected distance between adistance measuring device and an obstacle, a computer program and adistance detecting device for performing this method, which permitcalculation of the shortest projected distance even when this point isoutside of the detecting range of the distance measuring device.

This object is achieved by the method claimed in claim 1. This method ischaracterized by the following steps: Storing a limit time when thenearest point of the obstacle disappears from the detecting range of thedistance measuring means as the distance measuring device and theobstacle approach each other; storing a projected limit distance betweenthe nearest point of the obstacle and the distance measuring device atthe limit time; and detecting the projected distance between the nearestpoint of the obstacle and the distance measuring device, thereby takinginto consideration the limit distance, the limit time and informationabout the relative motion between the distance measuring device and theobstacle as long as the nearest point of the obstacle is outside of thedetecting range of the distance measuring device.

The claimed method advantageously permits calculation of therespectively shortest projected distance between the obstacle and thedistance measuring device even when the nearest point on the surface ofthe obstacle is outside of the detecting range of the distance measuringdevice. This calculation can be performed in accordance with theinvention when a limit distance, a limit time and information about therelative motion between the distance measuring device and the obstacleare known. The nearest point of the obstacle is that point on thesurface of the obstacle which has the shortest projected distance fromthe distance measuring device of all points of the obstacle. Projecteddistance thereby designates the length of projection of the directseparation between the nearest point P and the distance measuring devicealong a horizontal line. The terms limit time and limit distance used inthe present invention have the meanings defined in the previousparagraph.

The distance and, in particular, the projected distance between thenearest point P and the distance measuring device is advantageouslydetermined on the basis of information about the position and, inparticular, about the height of the nearest point above ground. Thisinformation about the position or height is determined e.g. by adistance detecting device as long as the nearest point of the obstacleis still within the detecting range of the distance measuring device.

Further advantageous embodiments of the method are the subject matter ofthe dependent claims.

The above-mentioned object of the invention is also achieved by acomputer program including program code and a distance detecting device.The advantages of these two solutions correspond to the advantagesmentioned above with respect to the claimed method.

The description includes a total of two figures, wherein

FIG. 1 shows the structure of an inventive distance detecting device;

FIG. 2 a shows detection of the distance between a nearest point P and adistance measuring device when the nearest point is within the detectingrange of the distance detecting device;

FIG. 2 b shows calculation of the projected distance between the nearestpoint P and the distance measuring device when the nearest point is atthe edge of the detecting range; and

FIG. 2 c shows determination of the projected distance between thenearest point P and the distance detecting device if the nearest point Pis outside of the detecting range of the distance detecting device.

The invention is explained in more detail below by embodiments withreference to the figures and their descriptions. FIG. 1 shows thestructure of the inventive distance detecting device 100. It ispreferably disposed in a vehicle 50 at a level of h_(s) above ground orabove a road (FIG. 2 a). It comprises a distance measuring device 110,e.g. in the form of an ultrasound or radar sensor for detecting thedistance between the distance measuring device 110 and an obstacle 200in the vicinity of the distance measuring device 110. The invention isbased on the assumption that the maximum height h_(p) of the obstacle200 above ground or above the road surface (FIG. 2 b) is less than theheight h_(s) of the installation position of the distance measuringdevice 110 in the vehicle 50. This precondition must be met since onlythen it is ensured that a nearest point P of the obstacle 200 having theshortest projected distance of all points of the obstacle from thedistance measuring device 110, can lie between the nearest point and thedistance measuring device 110 and also within or outside of thedetecting range of the distance measuring device, depending on the sizeof the actual distance.

The distance detecting device 100 also comprises a first storage element120 for storing a limit time when the nearest point P of the obstacle200 exits the detecting range of the distance measuring device 110 asthe distance measuring device 110 approaches the obstacle 200. Thedistance detecting device 100 also comprises a second storage elementfor storing a projected limit distance d_(Gr) between the nearest pointP of the obstacle 200 and the distance measuring device 110 at the limittime.

The distance detecting device moreover comprises a distancedetermination means 140 to detect distance information about relativemotion between the distance measuring device 110 and the obstacle 200,in particular, after the limit time, i.e. when the nearest point P ofthe obstacle 200 is outside of the detecting range of the distancemeasuring device 110. This distance determination means is preferablyinstalled in a vehicle 50 together with all of the components of thedistance detecting device 100 described above. This is especiallyreasonable when the vehicle is movable and an immovable stationaryobstacle is detected. The overall distance detecting device and, inparticular, the overall distance determination means may be disposed inthe obstacle 200 or be distributed between the vehicle 50 and theobstacle 200. It is only important that the distance determination meansis designed and arranged to detect relative motion between the distancemeasuring device 110 and the obstacle 200 irrespective of whether thedistance measuring device 110, the obstacle 200 or both move relative toeach other. The distance detecting device finally also comprises acalculating means 150 for detecting the projected distance d between thenearest point P of the obstacle 200 and the distance measuring device100. This calculating means 150 is designed to calculate this projecteddistance, thereby taking into consideration the limit distance d_(Gr)and information about the relative motion between the distance measuringdevice and the obstacle. In order to optimize the calculation, the limittime may also be taken into consideration.

The function of the distance detecting device 100 shown in FIG. 1 isdescribed in detail below with reference to the embodiments of FIGS. 2a, 2 b, and 2 c.

In order to illustrate the method, we assume that the vehicle 50 istravelling towards an immovable, i.e. stationary obstacle 200 at a speedV (see examples of FIGS. 2 a through 2 c). This is clearly only oneparticular kind of relative motion. Other relative motions include: onlythe obstacle 200 moves and the vehicle 50 does not move, or both thevehicle 50 and the obstacle 200 are moving. In FIG. 2, the installationheight of the distance measuring device 110 above the road is designatedwith h_(s). The point on the surface of the obstacle 200 having theshortest projected distance from the distance measuring device 110 isdesignated with P. The height of this point P above ground or above theroad is designated with h_(p).

FIG. 2 a shows a situation, wherein the distance between the distancemeasuring device 110 and the nearest point P of the obstacle 200 issufficiently large that the nearest point P is within the detectingrange of the distance measuring device 110. Suitable distanceinformation can then be easily determined, as originally envisioned.

As the vehicle 50 moves towards the presumably stationary obstacle 200at a speed V, the nearest point P moves increasingly out of the centerof the detecting range of the distance measuring device 110 until itfinally lies on its border as indicated in FIG. 2 b. In accordance withthe invention, the time at which this situation occurs is called thelimit time. The projected distance between the nearest point P and thedistance measuring device 110 at that time is called limit separation.The detection and storage of these limit values is essential for thepresent invention, since when the nearest point P is no longer withinthe detecting range of the distance measuring device 110, the distancebetween the nearest point P and the distance measuring device 110 canonly be calculated when these two limit values are known. The detectingrange of most distance measuring devices is defined by the position andthe opening angle of their radiation cone. When the portion a of theopening angle of the distance measuring device 110, which is below thehorizontal H, and the difference between the installation eight h_(s) ofthe distance measuring device 110 and the height h_(p) of the nearestpoint P are known, the limit distance d_(Gr) at the limit time can becalculated according to the following formula (1)

$\begin{matrix}{d_{Gr} = \frac{\tan (\alpha)}{h_{s} - h_{p}}} & (1)\end{matrix}$

A further approximation is obtained when e.g. the vehicle 50 continuesto move towards the obstacle 200. This relative motion is shown in FIG.2 c in the form of the distance dr which is determined by the distancedetermination means 140. The magnitude of this relative motion is ofinterest, in particular, starting from the limit time, at which thenearest point P of the obstacle 200 is no longer in the detecting rangeof the distance measuring device 110. The latter is indicated in FIG. 2c, wherein the nearest point P is no longer within the cone limited bythe angle α. In the situation shown in FIG. 2 c, the calculating means150 calculates the projected distance d between the nearest point P ofthe obstacle 200 and the distance measuring device 110 in accordancewith the invention through simple subtraction of the relative distancedr from the limit distance d_(Gr). This calculation method is validirrespective of the speed at which the obstacle moves, after detectionof its nearest point, completely out of the detecting range of thedistance measuring device 110. This occurs sooner for narrow obstaclesthan for wide obstacles.

In case of wide obstacles (obstacle 200 in FIG. 2 c), parts of theobstacle 200 are still detected even when the nearest point P is nolonger in the detecting range. This is indicated in FIG. 2 c, as theradiation cone of the distance measuring device 110 contacts theobstacle 200 on its upper surface at point B. An interpretation of theprojected distance d_(B) of this point as being the shortest distancebetween the obstacle 200 and the distance measuring device 110 would bewrong as is shown by a comparison with the correct projected distance d(also shown in FIG. 2 c), and could result in an undesired collisionbetween the vehicle 50 and the obstacle 200. The distance d is theactual shortest distance.

The above described and claimed method for detecting the projecteddistance between a distance measuring device 110 and an obstacle 200 inaccordance with the invention is preferably realized in the form of acomputer program which may run on a suitable computer, in particular, amicroprocessor. The computer program may optionally be stored on acomputer-readable data carrier together with further computer programs.The data carrier may be a disc, a compact disc (so-called CD), a flashmemory or the like. The computer program stored on the data carrier maybe transmitted and sold to a customer as a product. The computer programmay also be transmitted and sold as a product to a customer without theaid of a data carrier, e.g. via an electronic communications network.The communications network may e.g. be the Internet.

1-6. (canceled)
 7. A method for detecting a projected distance between adistance measuring device and an obstacle, the obstacle having a maximumheight which is smaller than a height (h_(s)) of the distance measuringdevice, the obstacle also having a predetermined nearest point (P) on asurface thereof having a shortest projected distance (d) from thedistance measuring device of all points of the obstacle, the methodcomprising the steps of: a) storing a projected limit distance (d_(Gr))between the nearest point (P) of the obstacle and the distance measuringdevice at a limit time at which the nearest point (P) of the obstaclemoves out of a detecting range of the distance measuring device, as thedistance measuring device and the obstacle approach each other; and b)evaluating the limit distance (d_(Gr)) and additional informationconcerning a relative motion between the distance measuring device andthe obstacle to determine projected distances (d) between the nearestpoint (P) of the obstacle and the distance measuring device as long asthe nearest point (P) is outside of the detecting range of the distancemeasuring device.
 8. The method of claim 7, wherein the position and theheight (h_(p)) of the nearest point (P) of the obstacle are determinedusing information provided by the distance measuring device as long asthe nearest point (P) of the obstacle is within the detecting range ofthe distance measuring device.
 9. The method of claim 7, furthercomprising determining the distance between the nearest point (P) andthe distance measuring device using information provided by the distancemeasuring device as long as the nearest point (P) of the obstacle iswithin the detecting range of the distance measuring device.
 10. Themethod of claim 7, wherein the detecting range is substantially definedby an opening angle of the distance measuring device, and the limitdistance (d_(Gr)) for the obstacle, having a height (h_(p)) at thenearest point above ground corresponding to the maximum total height ofthe obstacle, is calculated according to the following formula:$d_{Gr} = \frac{\tan (\alpha)}{h_{s} - h_{p}}$ wherein h_(s) is aheight of the distance measuring device above ground; and α is a portionof the opening angle of the distance measuring device below thehorizontal.
 11. The method of claim 7, wherein the distance measuringdevice is installed on a vehicle.
 12. A computer program includingprogram code for a distance detecting device, the program code beingstructured to carry out the method of claim
 7. 13. A distance detectingdevice, the device comprising: means for detecting a distance betweenthe distance measuring device and an obstacle in a vicinity of thedistance measuring device, the obstacle having a maximum height which issmaller than a height of the distance measuring device, the obstaclealso having a known nearest point which has a shortest projecteddistance of all points of the obstacle from the distance measuringdevice; means for storing a projected limit distance between the nearestpoint (P) of the obstacle and the distance measuring device at a limittime at which the nearest point (P) of the obstacle moves out of adetecting range of the distance measuring device, as the distancemeasuring device and the obstacle approach each other; a distancedetermination means for analysing distance information during relativemotion between the distance measuring device and the obstacle; and meansfor calculating a projected distance (d) between the nearest point ofthe obstacle and the distance measuring device, thereby taking intoconsideration a limit distance (d_(Gr)) and information provided by thedistance determination means.
 14. The device of claim 13, wherein thedevice is structured for use on a vehicle.
 15. The device of claim 13,wherein said distance determination means acts when the nearest point(P) of the obstacle is outside of a detecting range of the distancemeasuring device.